Millions of HIV-infected human patients suffer chronic pain. However, the pathological process leading to this devastating neurological condition is unclear, and an effective therapy is not available. Our long-term goals are to better understand the mechanism of HIV-associated pain and to develop rationale-based effective therapies. The objective of this application is to determine the role of glia, especially astrocytes, in the neuropathogenesis of HIV pain. In preliminary studies, we found that the HIV patients who developed chronic pain manifested dramatic astrocyte activation in the spinal cord dorsal horn (SCDH); this was not seen in the HIV patients who otherwise were similar but did not experience chronic pain. In this study, we aim to elucidate the mechanism and pathological significance of the astrocyte activation during the development of HIV gp120 (a major HIV neurotoxin protein)-induced pain in the mouse model. We propose that gp120 activates astrocytes in the SCDH through a mechanism that involves a neuron-to-astrocyte signaling protein, Wnt5a, and that the Wnt5a- regulated astrocyte activation promotes the development of gp120-induced pain. This hypothesis will be tested in three Specific Aims. In Aim #1, we will determine the requirement of neuronal Wnt5a in the SCDH for gp120 to induce astrocyte activation. In Aim #2, we will test the idea that Wnt5a activates astrocytes by stimulating a ROR2/JNK signaling pathway. In Aim #3, we will determine the involvement of Wnt5a-regulated astrocyte activation in the pathogenesis of gp120-induced pain in mice. The proposed research will use an integrated multidisciplinary approach of molecular and cell biology, pharmacology and conditional gene knockout. The results will provide important insights into the mechanism of astrocyte activation and its pathogenic role in HIV- associated chronic pain. The knowledge obtained is expected to facilitate the development of rationale-based medicine for HIV-associated chronic pain.